Bulk convert images to PDF: hundreds of photos without crashing the tab

Why big sets fail, in any tool

A browser tab works inside a fixed slice of memory. getPDF’s engine assumes at most 1.8 GB, and less on a device that reports less memory or does not report it at all (Safari and Firefox do not, so the tool assumes 1.5 GB). A phone’s tab can be stopped well before that, with no message, by the phone itself.

Photos eat that slice fast. A 12 megapixel photo is about 3 MB as a JPG and about 48 MB as raw pixels once decoded (4032 by 3024 pixels, 4 bytes each). A converter that decodes every photo and holds the pixels runs out of room after a few dozen photos, which is why so many online and app converters give up with a vague error at 30 or 50 pictures.

How getPDF stretches the limit

• JPG photos are never decoded. PDF can hold a JPG as it is, so the converter copies each photo’s picture data into the file unchanged. The 48 MB of raw pixels never exist; a 3 MB photo costs about 3 MB.
• Other formats are decoded 1 at a time. HEIC, PNG, WebP and the rest are decoded, stored, and the pixels let go before the next one starts.
• The finished file is checked before you get it. The tool opens the new PDF in its engine to confirm the page count and that the first page draws. That check needs memory for about twice the file’s size, and it is what sets the ceiling.

What stays: every photo of the job is read into memory before the work starts, and the photos, the PDF being written and the engine’s check copy all exist at the same moment. Measured in node on our test laptop with the same code the browser runs:

When it stops, the message names the cause: the PDF “was made, but it is too big for this browser to check”, how much memory the check needs against what the browser has, and “Make it in smaller parts (fewer files at a time) and merge them.” Nothing is offered half-checked. Split the set and it goes through. Time on a real device is longer than these numbers, because the browser first has to read every file from disk, and HEIC photos have to be decoded.

The staged method: batches, then 1 merge

1. Sort into folders of up to 100 photos (50 on a phone): batch-01, batch-02, batch-03. Numbered folder names keep the batches in order everywhere.
2. Convert batch 1. Drag the batch-01 folder onto JPG to PDF, or use “or a whole folder” under the drop zone. A folder’s photos are sorted by name the way people count, so photo-2 comes before photo-10, and files that are not pictures are left out (the page says how many).
3. Check the options once: Paper, Orientation, Margin and Fit apply to every page. Use the same settings for every batch, or the joins will show.
4. Make the PDF, download it, rename it to match the batch: part-01.pdf. Press Start over and repeat for each folder.
5. Compress the parts now, if the result is for sending (see below). It is much easier on parts than on the finished giant.
6. Open Merge PDF, drop all the parts, check the list reads part-01, part-02, part-03 (Up and Down fix it) and press Merge. On our laptop, 2 parts of 100 photos (297 MB each) merged into 1 PDF of 594 MB and 200 pages in 2.5 seconds.

Keeping the order across batches

• Leading zeros in the file names. 0001.jpg to 0300.jpg sorts the same in every program. Camera names such as IMG_20261011_101512.jpg already sort by time.
• 1 folder per batch, numbered. Drop 1 folder at a time; files picked by hand arrive in whatever order the picker hands over, which you then have to check.
• Check the seams after merging. Open the merged PDF and look at the last page of each part and the first page of the next: pages 100 and 101, 200 and 201. A batch merged in the wrong place shows up right there. If it did, organise the pages instead of starting over.

Output size, worked through

JPG photos go into the PDF as they are, plus about 640 bytes per page, so the PDF weighs what the photos weigh: 300 photos at 3 MB make about 890 MB. That is fine for an archive on a disk and useless for anything else. No mailbox takes it, and a viewer needs a long time to show 300 full-size photos.

So decide what the file is for:

• To send or upload: compress each part with Compress PDF before merging. On the Email preset our 20-photo PDF went from 60.7 MB to 2.2 MB, about 110 KB a photo, so 300 photos would come to roughly 33 MB, and the Web preset keeps more detail at a larger size. The make a PDF smaller guide covers the trade-offs.
• To print as a book or album: keep full quality, and give the printer the parts rather than 1 giant file if they accept several.
• To keep: keep the parts. 3 files of 300 MB are easier to copy, back up and open than 1 of 900 MB.

The honest part: when a PDF is the wrong container

A PDF is good at an ordered set someone will page through: a site survey, a claim, an album. It is a poor archive. Past a few hundred full-size photos, every way of using the file gets slow: opening, scrolling, emailing, even backing up.

For 1,000 photos, a zipped folder or a shared cloud folder serves better: every photo stays a separate file at full quality, the receiver opens only what they need, and nothing has to fit in a browser tab. If someone insists on 1 PDF, compress first and expect a file of about 110 MB on the Email preset.

This converter also does not choose, crop or straighten photos for you, and it does not make text in them searchable; run OCR PDF on a part if you need that. Everything above runs on your device, so even a 300-photo set is never uploaded. For smaller sets the combine photos guide is the quicker read.